System for distributing compressed air in a combustor

ABSTRACT

A system for distributing compressed air in a combustor of a gas turbine engine. The system may include a flow splitter, a center duct, an outer duct, and an inner duct configured to separate and receive compressed air from a prediffuser exit, and to route separate flows of the compressed air to separate downstream locations for the combustion reaction and for cooling. The system may include an axial mixer configured to axially receive a flow of the compressed air and to direct the flow to mix with fuel provided by an injector.

TECHNICAL FIELD

The present disclosure generally pertains to a combustor in a gas turbine engine, and is more particularly directed toward a system for distributing compressed air in a gas turbine engine combustor.

BACKGROUND

Gas turbine engines typically include a diffuser downstream of the compressor. The diffuser's purpose is to reduce the high velocity exit flow from the compressor to velocities suitable for combustion while recovering as much of the velocity head as static pressure as possible. After flowing through a prediffuser, the compressed air is dumped into the rapidly expanding area surrounding the combustion liner.

Presently, U.S. Pat. No. 4,527,386 issued to Markowski on Jul. 9, 1985 shows a diffuser for gas turbine engine. In particular, the disclosure of Markowski is directed toward a diffuser system including a prediffuser and a piping system that diverts the flow into two streams. One stream captures the prediffuser discharge air at the center of the gas path where the total pressure is at its highest level and provides an additional stage of diffusing before dumping it around the burner to supply liner cooling air, turbine cooling air and if necessary, small amounts of dilution air to trim radial temperature profile. The other stream is ducted directly into the burner avoiding the typical dump diffuser losses.

The present disclosure is directed toward overcoming known problems and/or problems discovered by the inventors.

SUMMARY

A system for mixing fuel and air in a gas turbine engine is disclosed herein. The system includes a center duct including a center duct inlet, the center duct configured to be coupled, for example pneumatically coupled to the prediffuser exit at the center duct inlet and extend downstream of the prediffuser exit, the center duct is further configured to receive a center flow of compressed air from the prediffuser exit, the center flow being separated away from an outer flow and an inner flow of air from the prediffuser exit, the outer flow also being radially outward and the inner flow being radially inward from the center flow, relative to the center axis, the center duct further configured to route the center flow to a combustion chamber of the gas turbine engine. The system also includes an axial mixer configured to axially receive the center flow of compressed air and to direct the center flow to mix with fuel provided by the injector.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary gas turbine engine.

FIG. 2 is a cutaway side view of a combustor in the gas turbine engine of FIG. 1.

FIG. 3 is a cutaway axial view along line 3-3 of FIG. 2.

FIG. 4 is an isometric view of an exemplary embodiment of a ducting module attached to a portion of a prediffuser of the combustor in FIG. 2.

FIG. 5 is an isometric view of a planar lobed mixer forming vortex pairs.

DETAILED DESCRIPTION

The present disclosure relates to a system for distributing compressed air in combustor that selectively extracts a high velocity core of a prediffuser exit flow for combustion, and provides additional diffusion and pressure recovery of lower velocity outer regions of the prediffuser exit flow. A ducting network is placed at the prediffuser exit such that the desired portion of the high velocity core and the lower velocity outer regions are separated and ducted as desired.

FIG. 1 is a schematic illustration of an exemplary gas turbine engine. Some of the surfaces have been left out or exaggerated (here and in other figures) for clarity and ease of explanation. The disclosure may reference an axis of rotation of the gas turbine engine (“center axis” 95), which may be generally defined by the longitudinal axis of its shaft 120. The center axis 95 may be common to or shared with various other engine concentric components. All references to radial, axial, and circumferential directions and measures refer to center axis 95, unless specified otherwise, and terms such as “inner” and “outer” generally indicate a lesser or greater radial distance from, wherein a radial 96 may be in any direction perpendicular and radiating outward from center axis 95.

In addition, the disclosure may reference a forward and an aft direction. Generally, all references to “forward” and “aft” are associated with the flow direction of primary air (i.e., air used in the combustion process), unless specified otherwise. For example, forward is “upstream” relative to primary air flow (i.e., towards the point where air enters the system), and aft is “downstream” relative to primary air flow (i.e., towards the point where air leaves the system).

Generally, the gas turbine engine 100 includes an inlet 110, a shaft 120 (supported by bearings 150), a compressor 200, a combustor 300, a turbine 400, an exhaust 500, and a power output coupling 600. The compressor 200 includes one or more compressor rotor assemblies 220. The turbine 400 includes one or more turbine rotor assemblies 420.

The combustor 300 includes a combustor case 310, an inner bearing housing 311, a plurality of struts 312, an outer shroud 314, an inner shroud 316, a plurality of injectors 350, and a combustion chamber 390. The combustor case 310 and the inner bearing housing 311 may be concentric clamshell casings forming a generally annular cavity there between and extending from the compressor 200 to the turbine 400. The combustor case 310 and the inner bearing housing 311 may be joined together by the plurality of struts 312. The combustion chamber 390 or “liner” is located within the annular cavity and is configured to withstand the high pressures and temperatures associated with combustion.

The outer shroud 314 and the inner shroud 316 define regions outside the combustion chamber 390 where air may be directed for cooling. In particular, the outer shroud 314 may be radially outward from the combustion chamber 390 and the inner shroud 316 may be radially inward from the combustion chamber 390. For example the outer shroud 314 and/or the inner shroud 316 may include ducting configured to bring compressed air to the combustion chamber 390 and may be tailored for heat exchange. According to one embodiment, the outer shroud 314 may include portions of the combustor case 310 and/or the inner shroud 316 may include portions of the inner bearing housing 311, for example, where an inner wall of either is configured to bring compressed air to the combustion chamber 390 for cooling.

In operation, air enters the inlet 110 as a “working fluid”, and is compressed by the compressor 200. In the compressor 200, the working fluid is compressed in an annular flow path by a series of compressor rotor assemblies 220. Once compressed, air leaves the compressor 200, it enters the combustor 300, where it is diffused and fuel is added. Fuel and some of the air are injected into the combustion chamber 390 via injector 350 and ignited. Some of the air is routed for cooling. After the combustion reaction, energy is then extracted from the combusted fuel/air mixture via the turbine 400 by a series of turbine rotor assemblies 420. Exhaust gas leaves the system via the exhaust 500.

The fuel delivered to combustor 300 may include any known type of hydrocarbon based liquid or gaseous fuel. Liquid fuels may include diesel, heating oil, JP5, jet propellant, or kerosene. In some embodiments, liquid fuels may also include natural gas liquids (such as, for example, ethane, propane, butane, etc.), paraffin oil based fuels (such as, JET-A), and gasoline. Gaseous fuels may include natural gas. In some embodiments, the gaseous fuel may also include alternate gaseous fuels such as, for example, liquefied petroleum gas (LPG), ethylene, landfill gas, sewage gas, ammonia, biomass gas, coal gas, refinery waste gas, etc. This listing of liquid and gaseous fuels is not intended to be an exhaustive list but merely exemplary. In general, any liquid or gaseous fuel known in the art may be delivered to combustor 300 through injector 350.

Similarly, one or more of the above components (or their subcomponents) may be made from stainless steel and/or durable, high temperature materials known as “superalloys”, or a variety of ceramic structures. A superalloy, or high-performance alloy, is an alloy that exhibits excellent mechanical strength and creep resistance at high temperatures, good surface stability, and corrosion and oxidation resistance. Superalloys may include materials such as HASTELLOY, INCONEL, WASPALOY, RENE alloys, HAYNES alloys, INCOLOY, MP98T, TMS alloys, and CMSX single crystal alloys. Ceramic structures may include monolithic components and/or ceramic/ceramic and ceramic/metal matrix components.

FIG. 2 is a cutaway side view of the combustor in the gas turbine engine of FIG. 1. For clarity and illustration purposes, certain features/components have been added, removed, and/or modified. As illustrated, the compressor 200 terminates at the compressor discharge 290, located at its downstream end. The compressor discharge 290 may form an annular passageway through which high velocity compressed air may exit the compressor 200. The compressor discharge 290 is coupled, for example fluidly coupled, to a prediffuser 320.

The prediffuser 320 includes a prediffuser inlet 321 and a prediffuser exit 322. The prediffuser inlet 321 is fluidly coupled to the compressor discharge 290. The prediffuser 320 is configured to diffuse compressed, high velocity compressed air exiting the compressor 200 in a stable and controlled manner. The prediffuser exit 322 is fluidly coupled to a combustor air duct network 330. The combustor air duct network 330 is placed at the exit of the prediffuser 320.

The combustor air duct network 330 includes a plurality of ducts forming discrete air passageways or channels. In particular, each duct segregates a flow in the duct from other, external flows. The combustor air duct network 330 is configured to receive compressed air from the prediffuser 320 and route it to predetermined locations. The combustor air duct network 330 may divide portions of the compressed air or may receive the compressed air in separate flows split by a downstream flow separator. Each air passageway may be smooth, of any convenient cross section, and shaped to mitigate losses (e.g., from flow separation) during routing. Together the ducts may form a separator configured to separate and distribute compressed air exiting the prediffuser 320 while mitigating losses after leaving the prediffuser 320 (e.g., dump losses).

According to one embodiment, the combustor air duct network 330 may include one or more flow splitters or dividers. The flow splitters or dividers may be radially and/or circumferentially oriented. For example, a radially oriented flow divider may be configured to divide the prediffuser exit 322 into annular sectors, each having a radially distributed velocity profile of compressed air. The radially distributed velocity profile of each annular sector may be markedly slower proximate an outer wall 323 and an inner wall 324 of the prediffuser 320 (e.g., slower due to boundary layer build up, diffusion recovery, etc.) than between the outer wall 323 and inner wall 324 (e.g., representing a minimally diffused central flow).

Also for example, a circumferentially-oriented flow splitter 337 (FIG. 4) may be configured to separate a center flow away from an outer flow and an inner flow prior to entering a duct. Here, the outer flow is radially outward and the inner flow is radially inward from the center flow, relative to the center axis 95. For example the center flow may include a portion of compressed air having an average velocity that is higher than the average velocity the outer flow and the inner flow when leaving the prediffuser exit 322. Also for example, the center flow may include a portion of compressed air leaving the prediffuser exit 322, where the ratio of flow velocity/average velocity, along a radial velocity profile, is greater than or equal to unity.

The ducts may be independent ducts or shrouds, forming the air passageways. Alternately, one or more ducts may be combined with other ducts so as to form a duct manifold, the duct manifold having a plurality of air passageways. The ducts or duct manifolds may be fixed to, or integrated into internal portions of the combustor 300, and/or coupled to other internal components. In addition, the ducts or duct manifolds may be uninterrupted or made up of joined sections between inlet and exit. Moreover, one or more sections of the ducts or duct manifolds may be integrated into one or more other components (e.g., the injector 350, the outer shroud 314, the inner shroud 316, etc.).

FIG. 3 is a cutaway axial view along line 3-3 of FIG. 2. According to one embodiment, the combustor air duct network 330 may be made up of a plurality of ducting modules 331. In particular, the combustor air duct network 330 may be made up of groups of ducts joined together, each group forming a ducting module 331 including portion of the total air passageways in the combustor air duct network 330. Likewise, the combustor air duct network 330 may be made up of a plurality of duct manifolds, each duct manifold forming a ducting module 331 including a portion of the total air passageways in the combustor air duct network 330.

Each ducting module 331 may be supported within the combustor 300 by any convenient means or combination of supports. For example, the ducting module 331 may be supported at each end of each of its respective air passageways. Also for example the ducting module 331 may be supported by internal structures fixed to the combustor case 310, the inner bearing housing 311, and/or the struts 312. Also for example the ducting module 331 may be supported by other internal components, such as the outer shroud 314, the inner shroud 316, the injector 350, the combustion chamber 390, and/or other ducting modules 331.

According to one embodiment, the ducting modules 331 may be arranged or otherwise coordinated with each other to form an annular array that is fluidly coupled to the prediffuser exit 322. As illustrated, the combustor air duct network 330 may be made up of a plurality of ducting modules 331 circumferentially distributed about the center axis 95. Each ducting module 331 may occupy an annular sector of the combustor 300. For example, each ducting module 331 may be coupled, for example pneumatically coupled, with the prediffuser exit 322, and segregate out an annular sector of flow exiting the prediffuser 320. Also for example, each ducting module 331 may pneumatically couple downstream with flow paths radially inward from, radially outward from, and into the combustion chamber 390, again occupying an annular sector of the combustor 300.

For example, the combustor air duct network 330 may include a separate ducting module 331 for each injector 350. Accordingly, where the combustor has twelve injectors 350, as illustrated, the combustor air duct network 330 may include twelve ducting modules 331, where the flow leaving prediffuser exit 322 is distributed to the twelve ducting modules 331. Also, groupings (pairs, as illustrated here) of the ducting modules 331 may be installed between and/or attached to struts 312 within the combustor case 310.

FIG. 4 is an isometric view of an exemplary embodiment of a ducting module attached to a portion of a prediffuser of the combustor in FIG. 2. In particular, one ducting module 331 (simplified, without diffusion or an intermediate duct) is shown pneumatically coupled with the prediffuser exit 322, without the other ducting modules 331 installed. For clarity and to illustrate the separation of flow into separate streams, only the trailing edge of the prediffuser 320 (including prediffuser exit 322) is shown. The view is generally looking downstream.

As illustrated, compressed air leaving the prediffuser exit 322 may be divided among the ducting modules 331. In particular, the flow may be divided by members of the prediffuser exit 322 and/or members of the ducting modules 331. For example, the prediffuser 320 may include internal struts that extend to the prediffuser exit 322 and align with the inlets of each ducting module 331, splitting the exiting flow in the circumferential direction 339.

Also as illustrated, compressed air leaving the prediffuser exit 322 may be split among the individual channels or ducts within each ducting module 331. In particular, the system for distributing compressed air may include a flow splitter 337. For example the flow splitter 337 may be configured to separate a center flow away from an outer flow and an inner flow of compressed air from the prediffuser exit 322, the outer flow being radially outward and the inner flow being radially inward from the center flow, relative to the center axis 95.

The center flow may include a region of compressed air having a higher average velocity than the outer and the inner flows. The positions of the individual splitters within the flow splitter 337 may be located such that the desired portion of the high velocity minimally diffused central core of the radial profile (center flow) is directed into a suitably constructed channel or duct. Likewise, the positions of the splitters may also be located such that the inner flow and the outer flow are similarly directed into suitably constructed channels or ducts, these ducts may be configured to both direct the flow and/or provide additional diffusion of the flow. The positioning of the various splitters may be determined by the flow requirements of the areas and devices being fed by the various channels of ducts.

The flow splitter 337 is located proximate to the prediffuser exit 322. In particular the flow splitter 337 may be located at the interface of the prediffuser exit 322 and the ducting module 331. In addition, the flow splitter 337 may be integrated into the prediffuser exit 322, the ducting module 331, and/or be an independent component. For example, the flow splitter 337 may be made up of the various duct inlets of the ducting module 331 at the interface with the prediffuser exit 322. Also for example, each ducting module 331 may include a plurality of ducts positioned radially adjacent to each other so as to split the exiting flow in the radial direction 338 and among each duct of the ducting module 331. In addition, the flow splitters 337 may extend upstream of the prediffuser exit 322 into the prediffuser 320. In this way, the flow splitter 337 may configured to separate the center flow away from the outer flow and the inner flow while still within the prediffuser 320.

According to one embodiment, each ducting module 331 may include an outer duct 332, an inner duct 333, and a center duct 334. Together, the outer duct 332, the inner duct 333, and the center duct 334 provides flow egress from an associated annular sector of the prediffuser exit 322. Moreover, this arrangement may direct a high velocity core of compressed air exiting the prediffuser 320 with its substantially higher pressure head or higher total pressure into a fuel/air mixing device that can take advantage of the higher energy flow. This arrangement may also be configured to aid in controlling the lower velocity flow for the provisioning of cooling air to the inner and outer walls of the combustion chamber 390 (also see FIG. 3, showing the downstream or egress ends of the outer ducts 332, the inner ducts 333, and the center ducts 334, distributed about center axis 95).

Returning to FIG. 2, the outer duct 332 may include an outer duct inlet 341 and an outer duct exit 342. The outer duct 332 is configured to be coupled, for example pneumatically coupled with the prediffuser exit 322 at the outer duct inlet 341. The outer duct 332 is further configured to receive an outer flow of compressed air from the prediffuser 320 during operation, and to route the outer flow to a radially outward portion of the combustor 300, relative to the center axis 95. For example, the outer duct 332 may be configured to route the outer flow to an outer side of the combustion chamber 390, relative to the center axis 95. Also for example, the outer duct 332 may be configured to be pneumatically coupled to the outer shroud 314 at the outer duct exit 342.

The pneumatic couple to the prediffuser exit 322 may be formed by mounting the outer duct inlet 341 to the prediffuser 320, or otherwise positioning the outer duct inlet 341 proximate the prediffuser exit 322. In addition, the pneumatic couple may be formed in combination with pneumatic couples of adjacent duct inlets and/or adjacent ducting modules 331, where egress from the prediffuser exit 322 is limited to the outer duct inlet 341 and the adjacent duct inlets and/or adjacent ducting modules 331. The pneumatic couple may also be formed in combination with flow separators located at or upstream of the prediffuser exit 322.

The outer flow may be defined as a lower velocity flow region exiting the prediffuser 320 proximate the outer wall 323 of the prediffuser 320, and with respect to the portion or annular sector of the prediffuser exit 322 associated with the ducting module 331. In particular, the outer flow includes boundary layer air associated with the outer wall 323 of the prediffuser 320. In addition, the outer flow may include recovered air.

For example, the outer duct inlet 341 may be configured to receive the outermost quarter of a radial span of the prediffuser exit 322, with respect to the portion or annular sector of the prediffuser exit 322 associated with the ducting module 331. Also for example, the outer duct inlet 341 may be configured to receive the radially outermost quarter of a flow velocity profile associated with the ducting module 331. Also for example, the outer duct inlet 341 may be configured to receive a radially outward portion of the flow velocity profile associated with the ducting module 331 that is below its average velocity.

According to one embodiment, the outer duct 332 may be configured to further diffuse the outer flow. In particular, the outer duct 332 may increase its effective flow area from the outer duct inlet 341 to the outer duct exit 342. The increase in effective flow area may be gradual, or otherwise limited such that a boundary layer does not separate from the outer duct 332 during operation.

The inner duct 333 may include an inner duct inlet 343 and an inner duct exit 344. The inner duct 333 is configured to pneumatically couple with the prediffuser exit 322 at the inner duct inlet 343, as above. The inner duct 333 is further configured to receive an inner flow of compressed air from the prediffuser 320, and route the inner flow to a radially inward portion of the combustor 300, relative to the center axis 95. For example, the inner duct 333 may be configured to route the inner flow to an inner side of the combustion chamber 390, relative to the center axis 95. Also for example, the inner duct 333 may be configured to be pneumatically coupled to the inner shroud 316 at the inner duct exit 344.

The inner flow may be defined as a lower velocity flow region exiting the prediffuser 320 proximate the inner wall 324 of the prediffuser 320, and with respect to the portion or annular sector of the prediffuser exit 322 associated with the ducting module 331. In particular, the inner flow includes boundary layer air associated with the inner wall 324 of the prediffuser 320. In addition, the inner flow may include recovered air.

For example, the inner duct inlet 343 may be configured to receive the innermost quarter of a radial span of the prediffuser exit 322, with respect to the portion or annular sector of the prediffuser exit 322 associated with the ducting module 331. Also for example, the inner duct inlet 343 may be configured to receive the radially innermost quarter of a flow velocity profile associated with the ducting module 331. Also for example, the inner duct inlet 343 may be configured to receive a radially inward portion of the flow velocity profile associated with the ducting module 331 that is below its average velocity.

According to one embodiment, the inner duct 333 may be configured to further diffuse the inner flow. In particular, the inner duct 333 may increase its effective flow area from the inner duct inlet 343 to the inner duct exit 344. The increase in effective flow area may be gradual, or otherwise limited such that a boundary layer does not separate from the inner duct 333 during operation.

The center duct 334 may include a center duct inlet 345 and a center duct exit 346. The center duct 334 is configured to pneumatically couple with a portion of the prediffuser exit 322 offset from the outer wall 323 and the inner wall 324 via the center duct inlet 345, and extend downstream. The center duct 334 is further configured to receive a center flow of compressed air from the prediffuser exit 322, and route the center flow to a radially central portion of the combustor 300, between the inner and outer flows. For example, the center duct 334 may be configured to route the center flow to the injector 350. Each injector 350 of the combustor 300 may interface with and/or be integrated with an independent center duct 334. Also for example, the center duct 334 may be configured to route the center flow to the combustion chamber 390. Also for example, the center duct 334 may extend to, and pneumatically couple with, an injector port 392 of the combustion chamber 390.

According to one embodiment, the center duct 334 may be segmented. In particular, the center duct 334 may be segmented such that a first portion of the center duct 334 includes the center duct inlet 345, and a second portion of the center duct 334 includes at the center duct exit 346, with the first and second portions of the center duct 334 being pneumatically coupled together. For example, the first portion of the center duct 334 may be a plain duct member, whereas the second portion of the center duct 334 may be formed from or otherwise integrated into the injector 350. Moreover, the center duct 334 may include an aggregation of members pneumatically coupled and forming a continuous flow path. Also for example, the center duct 334 may be segmented for ease of manufacturability, ease of installation, etc.

The center flow may be defined as a higher velocity flow region exiting the prediffuser 320 away from both the outer wall 323 and the inner wall 324 of the prediffuser 320, and with respect to the portion or annular sector of the prediffuser exit 322 associated with the ducting module 331. In particular, the center flow excludes boundary layer air associated with the outer wall 323 and the inner wall 324 of the prediffuser 320. In addition, the center flow may include high velocity flow which may only be partially recovered air.

For example, the center duct inlet 345 may be configured to receive the center half quarter of a radial span of the prediffuser exit 322, with respect to the portion or annular sector of the prediffuser exit 322 associated with the ducting module 331. Also for example, the center duct inlet 345 may be configured to receive the fastest half of a flow velocity profile associated with the ducting module 331. Also for example, the center duct inlet 345 may be configured to receive the portion of the flow velocity profile associated with the ducting module 331 that is at or above its average velocity.

According to one embodiment, the center duct 334 may be configured to further diffuse the center flow. In particular, the center duct 334 may increase its effective flow area between the center duct inlet 345 to the center duct exit 346. The increase in effective flow area may be gradual or otherwise limited such that a boundary layer does not separate from the inner duct 333 during operation. According to one embodiment, center duct 334 may increase its effective flow area from the center duct inlet 345 to a predefined downstream location, and then hold the effective flow area constant until the center duct exit 346.

According to one embodiment, the center duct 334 may change in shape between the center duct inlet 345 and the center duct exit 346. In particular, the center duct 334 may have a complex shape, smoothly transforming from a quadrilateral flow cross section at the center duct inlet 345 to a round flow cross section at the center duct exit 346 (see FIG. 4, isometric view of the ducting module 331, showing the smooth transition between the center duct inlet 345 and the center duct exit 346). According to one embodiment, the center duct 334 may maintain a constant effective flow area throughout the transition. According to another embodiment, the center duct 334 may continuously increase its effective flow area from the center duct inlet 345 to the round flow cross section, being configured as a diffuser for the center flow as described above.

According to one embodiment, the ducting module 331 may further include an intermediate duct 335. The intermediate duct 335 may include an intermediate duct inlet 347 and an intermediate duct exit 348. In addition, the intermediate duct 335 may share a wall with at least one of the outer duct 332, the inner duct 333, and the center duct 334. For example, an outer surface (relative to an injector axis 359) of the center duct 334 may form an inner wall (relative to the injector axis 359) of the intermediate duct 335.

The intermediate duct 335 is configured to bleed off air from at least one of the outer duct 332, the inner duct 333, and the center duct 334 via the intermediate duct inlet 347. For example, the intermediate duct inlet 347 may include one or more bleed holes (or other perforations) through an outer wall of the center duct 334, the outer wall being with respect to the injector axis 359. Also for example, the intermediate duct inlet 347 may include one or more bleed holes (or other perforations) through an inner wall of the outer duct 332 and/or the inner duct 333, the inner wall also being with respect to the injector axis 359.

The intermediate duct 335 is further configured to route the bled air to a portion of the combustion chamber 390 such as a dome heat shield 393 for cooling. In particular, a portion of the combustion chamber 390 perpendicular to the exit of the injector 350 (liner dome) may be cooled in a conventional manner, such as with a strain isolated panel, which forms part of dome heat shield 393 and surrounds the injector port 392. For example, the intermediate duct exit 348 may be configured so that the bled air impinges on the dome heat shield 393 for cooling purposes.

According to one embodiment, the intermediate duct 335 may have a complex shape. In particular, the intermediate duct 335 may change between a generally round cross section (normal to the injector axis 359) to a polygonal cross section. For example and as illustrated, at an upstream end (relative to the injector axis 359), the intermediate duct 335 may have a round shape concentric and integrated with the center duct 334, and at a downstream end (relative to the injector axis 359), the intermediate duct 335 may have a generally quadrilateral shape that is separated and offset from the intermediate duct 335. The intermediate duct 335 may smoothly transition between the two shapes. Also, the intermediate duct 335 may change between a single chamber flow path and a dual or multi chamber flow path, for example, where other structures intervene in the flow path or otherwise create a discontinuity.

According to one embodiment, the ducting module 331 may further include an axial mixer 336 (“axial voracity generator” or “lobed mixer”). In particular, the axial mixer 336 is configured to axially receive the center flow of compressed air (relative to the injector axis 359, and as opposed to radially receiving). Moreover, the axial mixer 336 may form an inner wall of the center duct 334 such that the center flow of compressed air would travel in an annular flow path around the side of the mixer.

The axial mixer 336 may be further configured to direct the received center flow of compressed air to mix with a stream of fuel provided by the injector 350 on the opposite side of the annular space around the mixer, and to produce counter rotating vortex pairs (see FIG. 5) using fluid mechanic mechanisms at the exit. Moreover, the center duct 334 may be configured for low loss such that the center flow and the fuel stream 20 have a maximum velocity gradient, further increasing shear between the two fluids and thus mixing. In addition, the axial mixer 336 may be configured such that air and fuel are initially mixed upon entering the combustion chamber 390.

According to one embodiment, the axial mixer 336 may be configured in a circumferential form. In this configuration the axial mixer 336 may be adapted to the existing geometry and layout of the injector 350 and the rest of the ducting module 331. For example and as illustrated, the axial mixer 336 may include a lobed mixer including a plurality of alternating lobes 349 circumferentially distributed about the injector axis 359. Also for example, the lobed mixer may smoothly transition between a generally cylindrical or otherwise smooth round shape and the undulating lobed shape of its mixing features.

According to one embodiment, the circumferential lobed mixer may be arranged such that it is surrounded coaxially with center duct 334, which may be of constant or converging effective flow area to encourage the center flow to attach and remain attached to the surfaces of the lobes 349. According to one embodiment, the center duct 334 may increase its effective flow area from the center duct inlet 345 up to the lobes 349, and then hold the effective flow area constant until the center duct exit 346. Alternately, the center duct 334 may increase its effective flow area from the center duct inlet 345 up to the lobes 349, and then reduce the effective flow area across the lobes 349.

FIG. 5 is an isometric view of a planar lobed mixer forming vortex pairs. To aid in describing the axial mixer 336 above, a planar version of a lobed mixer is shown. Here, the planar lobed mixer 836 is configured to generate mixing from the interplay of both mechanical and viscous forces forming vortex pairs 813. As illustrated, planar lobed mixer 836 directs streams of a first fluid 811 and a second fluid 812 to cross downstream of the planar lobed mixer 836, which creates high levels of shear between the two fluid streams, and which generates the vortices responsible for mixing. These directed high shear flows create the vortex pairs 813 that mix the two fluids. Each pair of alternating lobes 849 produces a pair of vortices which subsequently entwine as the vortex pair 813, intimately mixing the first and the second fluid 811, 812.

With reference to FIG. 2 and FIG. 3, the axial mixer 336 is conceptually similar to the planar lobed mixer 836 shown in FIG. 5. Here however, as an axial lobed mixer, the axial mixer 336 directs streams of fuel and air to cross in a radial direction downstream of the axial mixer 336, which similarly creates high levels of shear between the two fluid streams, and which generates the vortices responsible for mixing. These directed high shear flows also create the vortex pairs that mix the two fluids. Similar to the lobes 849 of FIG. 5, here, each pair of alternating lobes 349 in the axial mixer 336 produces a pair of vortices which subsequently entwine, intimately mixing the fuel and air for the combustion reaction.

With reference to FIG. 2, according to another embodiment, the axial mixer 336 may be configured such that mixing features (e.g., lobes 349) of the axial mixer 336 are axially positioned upstream from the combustion chamber 390, relative to the injector axis 359. In particular, the mixing features may be recessed within the injector 350, the center duct 334, and/or any other sheltered area upstream of the combustion chamber 390. For example and as illustrated, the mixing features of the axial mixer 336 (represented by the triangular section at its downstream end) may extend up to the injector port 392 (the opening into the combustion chamber 390). Also for example, the axial mixer 336 may be recessed downstream (relative to the injector axis 359) of the injector port 392 and oriented such that a minimal aspect ratio is presented to the hot gas (e.g., downstream end running parallel to the injector axis 359). Additionally, the axial mixer 336 may be recessed such that air and fuel are pre-mixed within the center duct 334 prior to exiting the injector.

According to another embodiment, the ducting module 331 may be configured such that air exiting the intermediate duct 335 provides additional protection to the axial mixer 336. In particular, the intermediate duct exit 348 and/or the dome heat shield 393 may be configured such that cooling air is discharged after impinging on the dome heat shield 393 radially inward around the periphery of the axial mixer 336. In addition, the discharged cooling air may be aligned with mixing mechanism of the axial mixer 336 (e.g., air management lobes of a lobe mixer) to augment the flow, and therefore the shear between the fuel and air streams.

According to one embodiment, a ducting module 331 may be discontinuous for manufacturing or other design requirements. In particular, one of more of the outer duct 332, the inner duct 333, the center duct 334, the intermediate duct 335, and the axial mixer 336 may be integrated with other components. For example and as illustrated, a support arm 352 may pass through of the outer duct 332, the intermediate duct 335, the center duct 334, and the axial mixer 336 in order to position the injector on the injector axis 359. Also for example, the a first portion of ducting module 331 may be integrated with, or otherwise fixed to the prediffuser 320 while a second portion of the ducting module 331 may be integrated with the injector 350.

According to an alternate embodiment, the ducting of each ducting module 331 may be reversed from that described above. In particular, a desired portion of the higher velocity core of compressed air may be ducted to the inner and outer walls of the combustion chamber 390 for cooling. This arrangement may also duct the lower velocity flow (proximate the walls of the prediffuser 320) into the combustion chamber 390.

To illustrate, the inner and outer ducts may have inlets configured to interface with the prediffuser 320 as described above, but which merge into a single duct that is configured to direct the joined inner and outer flows to the combustion chamber 390. Additionally, the center duct may have an inlet configured to interface with the prediffuser 320 as described above, but which then splits into two separate ducts. The two separate ducts may be configured to route compressed air to the outer shroud 314 and the inner shroud 316, respectively and similarly to the outer duct 332 and inner duct 333 as described above. In addition, the separate ducts that direct this central core flow may have progressively increasing cross-sectional area and begin with little or no boundary layer on their walls, functioning as a post diffuser stage, and reducing the velocity and dynamic pressure head of the central core flow. Thus, the central core flow may be subsequently discharged into the liner shrouds with a substantially reduced dump loss, lower velocity (more fully recovered).

INDUSTRIAL APPLICABILITY

The present disclosure generally applies to gas turbine combustors, and gas turbine engines having a prediffuser. The described embodiments are not limited to use in conjunction with a particular type of gas turbine engine, but rather may be applied to stationary or motive gas turbine engines, or any variant thereof. Gas turbine engines, and thus their components, may be suited for any number of industrial applications, such as, but not limited to, various aspects of the oil and natural gas industry (including include transmission, gathering, storage, withdrawal, and lifting of oil and natural gas), power generation industry, aerospace and transportation industry, to name a few examples. In addition, the present disclosure may apply to furnace applications.

Generally, embodiments of the presently disclosed system for distributing compressed air in the combustor are applicable to the use, operation, maintenance, repair, and improvement of gas turbine engines, and may be used in order to improve performance and efficiency, decrease maintenance and repair, and/or lower costs. In addition, embodiments of the presently disclosed system for distributing compressed air in the combustor may be applicable at any stage of the gas turbine engine's life, from design to prototyping and first manufacture, and onward to end of life. Accordingly, the system for distributing compressed air in the combustor may be used as a retrofit or enhancement to existing gas turbine engine, as a preventative measure, or even in response to an event. This is particularly true as the presently disclosed system for distributing compressed air in the combustor may be installed in a combustor having identical interfaces to another combustor so as to be interchangeable with an earlier type of combustor.

In use, the system for distributing compressed air in a combustor forms a reduced-loss ducting network within the combustor. The leading edge of the ducts or splitters are located such that a desired portion of high velocity, minimally diffused central core of the radial profile of compressed air exiting the prediffuser is directed into the combustor duct network. The ducts that direct this central core flow may have progressively increasing cross-sectional area and begin with little or no boundary layer on their walls, functioning as a post diffuser stage, and reducing the velocity and dynamic pressure head of the central core flow. This central core flow may be subsequently discharged into the injector with a substantially reduced dump loss, lower velocity (more fully recovered). Alternately, this central core flow may be subsequently discharged into about the combustion chamber for cooling.

The preceding disclosure describes a combination of various technologies into a unique configuration for a gas turbine combustion system exhibiting low pressure losses and enhanced mixing capabilities. In particular, system for distributing compressed air in a combustor combines targeted-use flow splitting, low-loss ducting, supplemental diffusion, and axial mixing, which may result in improved diffuser recovery performance, lower pressure losses, enhanced mixing, and/or lower emissions. In addition, the system for distributing compressed air in a combustor may provide for an integrated system to manage fuel and air mixture preparation, reuse of spent cooling flows to augment mixing, and potentially shorter overall system lengths. By eliminating the traditional high pressure loss mixing devices currently employed in combustion systems and substituting low loss more efficient mixing devices lower overall systems pressure drops may be achieved with a corresponding increase in overall system efficiency.

By combining the aforementioned technologies, improved diffuser recovery performance and the low loss high mixing rate lobed mixer may be combined to deliver an advance fuel air management system. The coupling of these techniques in a combustion system is adaptable to existing engines, especially of the industrial nature since they often provide ample room for the additional hardware and are not necessarily constrained by length or weight limitations of aircraft engines.

The preceding detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. The described embodiments are not limited to use in conjunction with a particular type of gas turbine engine. Hence, although the present embodiments are, for convenience of explanation, depicted and described as being implemented in a stationary gas turbine engine, it will be appreciated that it can be implemented in various other types of gas turbine engines, and in various other systems and environments. Furthermore, there is no intention to be bound by any theory presented in any preceding section. It is also understood that the illustrations may include exaggerated dimensions and graphical representation to better illustrate the referenced items shown, and are not consider limiting unless expressly stated as such. 

What is claimed is:
 1. A gas turbine engine having a center axis and comprising: a compressor; a prediffuser pneumatically coupled to the compressor, the prediffuser including a prediffuser exit, an outer wall, and an inner wall; and a system for mixing fuel and air, the system including a flow splitter located proximate to the prediffuser exit and configured to separate a center flow away from an outer flow and an inner flow of compressed air from the prediffuser exit, the center flow having a higher average velocity than the outer flow and the inner flow, a center duct including a center duct inlet and a center duct exit, the center duct configured to pneumatically couple with a portion of the prediffuser exit offset from the outer wall and the inner wall at the center duct inlet, the center duct further configured to receive the center flow from the prediffuser exit and to route the center flow to a combustion chamber of the gas turbine engine, and an axial mixer within the center duct, the axial mixer configured to direct the center flow to mix with fuel provided by an injector.
 2. The gas turbine engine of claim 1, wherein an effective flow area of the center duct increases between the center duct inlet and the center duct exit.
 3. The gas turbine engine of claim 1, wherein the axial mixer includes a lobe mixer, the lobe mixer having a plurality of alternating lobes circumferentially distributed around an injector axis.
 4. The gas turbine engine of claim 3, wherein an effective flow area of the center duct increases between the center duct inlet and the plurality of alternating lobes; and wherein the effective flow area of the center duct hold the effective flow area constant or reduces the effective flow area between the plurality of alternating lobes and the center duct exit.
 5. The gas turbine engine of claim 1, wherein the center duct is further configured to extend to and pneumatically couple with the combustion chamber of the gas turbine engine.
 6. The gas turbine engine of claim 1, wherein the axial mixer is further configured to initially mix the center flow with the fuel upon entering the combustion chamber of the gas turbine engine.
 7. The gas turbine engine of claim 1, wherein the axial mixer is further configured to direct the center flow to pre-mix with the fuel upstream of the combustion chamber of the gas turbine engine.
 8. The gas turbine engine of claim 1, wherein the flow splitter extends upstream of the prediffuser exit into the prediffuser, the flow splitter further configured to separate the center flow away from the outer flow and the inner flow while within the prediffuser.
 9. The gas turbine engine of claim 1, wherein the center duct is configured such that the center flow only includes compressed air leaving the prediffuser exit having a velocity, along a radial velocity profile, that is greater than or equal to an average velocity of all compressed air leaving the prediffuser exit, along the radial velocity profile.
 10. A gas turbine engine having a center axis and comprising: a compressor; a prediffuser pneumatically coupled to the compressor, the prediffuser including a prediffuser exit, an outer wall, and an inner wall; and a combustor air duct network including a flow splitter located proximate to the prediffuser exit and configured to separate a center flow away from an outer flow and an inner flow of compressed air from the prediffuser exit, the outer flow being radially outward and the inner flow being radially inward from the center flow, relative to the center axis; a center duct including a center duct inlet and a center duct exit, the center duct configured to pneumatically couple with a portion of the prediffuser exit offset from the outer wall and the inner wall at the center duct inlet, the center duct further configured to receive the center flow from the prediffuser exit and to route the center flow to a combustion chamber of the gas turbine engine; and an outer duct including an outer duct inlet and an outer duct exit, the outer duct configured to pneumatically couple with the prediffuser exit at the outer duct inlet, adjacent to the center duct inlet, the outer duct further configured to receive the outer flow of compressed air from the prediffuser and to route the outer flow to an outer side of the combustion chamber, relative to the center axis; and an inner duct including an inner duct inlet and an inner duct exit, the inner duct configured to pneumatically couple with the prediffuser exit at the inner duct inlet, adjacent to the center duct inlet and opposite the outer duct inlet, the inner duct further configured to receive the inner flow of compressed air from the prediffuser and to route the inner flow to an inner side of the combustion chamber, relative to the center axis.
 11. The gas turbine engine of claim 10, wherein the center duct is further configured to extend to and pneumatically couple with an injector port of the combustion chamber.
 12. The gas turbine engine of claim 10, wherein a first portion of the center duct includes the center duct inlet and is configured to extend to an injector, and wherein a second portion of the center duct is integrated into the injector, the first and second portions of the center duct pneumatically coupled with each other.
 13. The gas turbine engine of claim 10, wherein the gas turbine engine has a plurality of injectors; and wherein the combustor air duct network includes a plurality of the center duct, each configured to interface one of the plurality of injectors.
 14. The gas turbine engine of claim 10, wherein an effective flow area of the center duct increases between the center duct inlet and the center duct exit.
 15. The gas turbine engine of claim 10, wherein the center duct is configured such that the center flow only includes compressed air leaving the prediffuser exit having a velocity, along a radial velocity profile, that is greater than or equal to an average velocity of all compressed air leaving the prediffuser exit, along the radial velocity profile.
 16. The gas turbine engine of claim 10, further comprising an intermediate duct including an intermediate duct inlet and an intermediate duct exit, the intermediate duct configured to bleed off air from the center duct via the intermediate duct inlet, the intermediate duct further configured to route the bled off air to a portion of the combustion chamber for cooling.
 17. The gas turbine engine of claim 10, further comprising an intermediate duct including an intermediate duct inlet and an intermediate duct exit, the intermediate duct configured to bleed off air from at least one of the outer duct and the inner duct, via the intermediate duct inlet, the intermediate duct further configured to route the bled off air to a portion of the combustion chamber for cooling.
 18. A gas turbine engine having a center axis and comprising: a compressor; a combustor coupled to the compressor, the combustor including a prediffuser pneumatically coupled to the compressor, the prediffuser including a prediffuser exit, an outer wall, and an inner wall; and a system for distributing compressed air in the combustor including a center duct including a center duct inlet, the center duct configured to be pneumatically coupled to the prediffuser exit at the center duct inlet and extend downstream of the prediffuser exit, the center duct further configured to receive a center flow of compressed air from the prediffuser exit, the center flow being separated away from an outer flow and an inner flow of compressed air from the prediffuser exit, the outer flow also being radially outward and the inner flow being radially inward from the center flow, relative to the center axis, the center duct further configured to route the center flow to a combustion chamber of the gas turbine engine; and an outer duct including an outer duct inlet and an outer duct exit, the outer duct configured to be pneumatically coupled to the prediffuser exit at the outer duct inlet and to receive the outer flow of compressed air from the prediffuser, the outer duct further configured to route the outer flow to an outer side of the combustion chamber, relative to the center axis; and an inner duct including an inner duct inlet and an inner duct exit, the inner duct configured to be pneumatically coupled to the prediffuser exit at the inner duct inlet and to receive the inner flow of compressed air from the prediffuser, the inner duct further configured to route the inner flow to an inner side of the combustion chamber, relative to the center axis. an axial mixer within the center duct, the axial mixer configured to direct the center flow to mix with fuel provided by an injector.
 19. The gas turbine engine of claim 18, wherein the axial mixer includes a lobe mixer, the lobe mixer having a plurality of alternating lobes circumferentially distributed around an injector axis.
 20. The gas turbine engine of claim 18, further comprising an intermediate duct including an intermediate duct inlet and an intermediate duct exit, the intermediate duct configured to bleed off air from the center duct via the intermediate duct inlet, the intermediate duct further configured to route the bled off air to a portion of the combustion chamber for cooling. 